John Boehner, the former Republican speaker of the House who once said he was “unalterably opposed” to decriminalizing marijuana laws, has joined a board of directors for a cannabis company with an eye on rolling back federal regulations.

The former Ohio congressman has been appointed to the board of advisers of Acreage Holdings, invoking the need for veterans to access the drug legally to explain his change of heart, Boehner said in a statement Wednesday. The company grows and sells legal weed and operates in 11 states.

FILE – In this Feb. 26, 2015, file photo, House Speaker John Boehner speaks during a news conference on Capitol Hill in Washington. Former U.S. House Speaker Boehner says he has had a change of heart on marijuana and will promote its nationwide legalization. Known as an avid cigarette smoker, the Ohio Republican has joined the advisory board of Acreage Holdings, a multistate cannabis company. (AP Photo/J. Scott Applewhite, File)

Boehner’s acceptance of marijuana tracks with evolving beliefs about the drug and its uses among Americans and even Republican lawmakers, Erik Altieri, executive director for the Washington-based marijuana advocacy group NORML, told The Washington Post.

But, he said, Boehner probably would have been more influential if he supported marijuana use for veterans while he was speaker. The Department of Veterans Affairs continues to struggle with treatment options for post-traumatic stress and other mental health conditions.

“It would’ve been more helpful for him advocating for this 10 years ago,” he said.

The move is a stark reversal for the former speaker, who in 2011 wrote a constituent that he was against “legalization of marijuana or any other FDA Schedule I drug,” adding that “I remain concerned that legalization will result in increased abuse of all varieties of drugs, including alcohol.”

Boehner reiterated his opposition to legalization as recently as September 2015. Nearly half a million people were arrested for selling weed during Boehner’s term as speaker from 2011-2015, Quartz reported.

“I have concluded descheduling the drug is needed so that we can do research and allow VA to offer it as a treatment option in the fight against the opioid epidemic that is ravaging our communities,” he said.

Spokesperson David Schnittger said Boehner’s evolving position has been the result of close study after leaving office.

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Currently, nine states plus Washington, D.C. have legalized recreational use of the drug, while many others allow some sort of medical use. The Justice Department has been prohibited from using federal funds to target state-legal medical marijuana businesses since 2014.

Boehner is joined on the board of advisers by former Massachusetts governor Bill Weld, a Republican who left office in 1997 and was former New Mexico governor Gary Johnson’s running mate in 2016 on the libertarian party ticket. As governor, Weld advocated for medical marijuana legalization since 1992.

It is unknown if Boehner or Weld hold paid positions on the board. Acreage Holdings spokesman Lewis Goldberg declined to discuss salary or benefits of its executives. Weld told Bloomberg he was considering an investment in the company.

Legal marijuana sales topped $9 billion in 2017, according to one industry estimate. Worldwide, legal marijuana could be a $57 billion industry by 2027, according to a report by Arcview Market Research.

Weld, a former federal prosecutor, said the conventional wisdom about marijuana during the Reagan administration was that it acted as a “gateway drug” to more harmful substances.

FILE – Former Massachusetts Gov. William Weld has joined the advisory board of Acreage Holdings, a multistate cannabis company. (AP Photo/Cheryl Senter, File)

“Now there’s some evidence that it can become an exit drug” and an alternative to opioid addiction, which has become the primary public health concern in Massachusetts, he said in an interview with The Post.

Weld said his advocacy will likely find appeal among conservatives who champion state laws to regulate issues without federal interference. A number of Republican lawmakers criticized a recent move by Attorney General Jeff Sessions to roll back a long-standing policy of federal noninterference with state-legal recreational marijuana laws.

Morgan Fox, a spokesperson for the pro-legalization Marijuana Policy Project, told the New York Times that Boehner “should be actively working to reform federal marijuana laws to allow states to determine their own policies, rather than just consulting with a business to navigate the conflicts between state and federal law.”

In a joint statement, Boehner and Weld focused on a long-standing concern among veterans and advocacy groups – federal law classifies marijuana as a Schedule I drug, the same as heroin and ecstasy.

Current prohibitions have stymied research at Veterans Affairs to evaluate the drug’s efficacy in treating post-traumatic stress and physical pain as the result of military service, then-VA Secretary David Shulkin said earlier this year. Critics of restrictions say a tangle of federal laws that regulate research and funding have confused VA and lawmakers on what it can evaluate.

Veterans advocating for decriminalizing marijuana have spoken with Boehner in the past, he said. “It was an argument he heard as a member, considered and never dismissed,” Schnittger said.

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Descheduling cannabis would not legalize it nationally, but it would end federal marijuana enforcement and allow states to set their own marijuana policies without federal interference.

Polls show that over 60 percent of Americans favor legalizing marijuana completely, with well over 90 percent in favor of legal medical use. Democrats eyeing a 2020 presidential run have grown increasingly vocal about the shortcomings of current federal law, and the cannabis industry has stepped up lobbying lawmakers in both parties.

Acreage Holdings, a main player in the increasingly white-collar marijuana trade, will expand its research initiatives among universities as it seeks to “demystify” cannabis, chief executive Kevin Murphy told The Post. The company cultivates, processes and distributes marijuana in the growing, billion-dollar industry, according to its site.

The company focused on veterans in its messaging because they are “passionate” about broadening marijuana options available to former troops, Murphy said.

The American Legion, the largest veterans group in the country, found in a 2017 survey that veterans overwhelmingly support marijuana use for medical reasons. About 22 percent of veteran households said they use weed for medical reasons.

Altieri said he hopes Boehner will use his influence within the GOP to extend acceptance of marijuana, which may lead to legalization laws for veterans and nonveterans alike. VA has said that 20 veterans commit suicide every day.

“Think of the number of veterans who could’ve had relief sooner,” he said.